Electroluminescent or EL panels having a large emitting surface area are thin, light-emitting devices that may be employed for illuminating a large surface, interior or exterior area, or room. The light is produced without the high temperatures associated with incandescent and fluorescent light-emitting devices. In addition since glass envelopes used for these types of lighting systems are not required for EL lighting systems, they are far less prone to breakage from contact with foreign objects. Electroluminescent (EL) lamps are created by placing a phosphor layer between two electrodes that function electrically as a capacitor. AC voltage is applied across the electrodes and light is generated which passes through the top transparent electrode. EL lamps can be as thin as 0.008″, are flexible, and are shock resistant. Flexible electroluminescent cable, sheets, and ribbons are known and can be cut to size and can include an adhesive mounting layer.
Area illuminators are typically controlled through wall-mounted switches, either binary or variable. Such arrangements, while simple, require additional equipment remote from the area illuminator for switching. Incandescent lamp holders that control the output of the lamp when a user touches the holder body are also known. Alternatively, EL lights may be switched on and off at a power supply or inline on the power cable.
Physical properties of the human body have been used to activate touch-sensitive switches that, in turn, have been used to active and deactivate lighting systems. There are four general techniques used to enable this capability.
Temperature—The human body is generally warmer than the surrounding air. Many elevators therefore use buttons that are sensitive to the warmth of the human finger. Also, switches using infrared detectors to sense the heat of the human body are known.
Resistance—The human body, being made mostly of water, conducts electricity reasonably well. By placing two contacts very close together, a finger can close an electrical circuit when touched.
Radio reception—Because the human body is conductive, it can act like an antenna. Some touch-sensitive switch designs simply look for a change in radio-wave reception that occurs when the switch is touched.
Capacitance—Conventional touch-sensitive lamps almost always use a fourth property of the human body, capacitance. The lamp, when standing by itself on a table, has a certain capacitance. This means that if a circuit tried to charge the lamp with electrons, it would take a certain number to “fill it.” When the lamp is touched by a human body, the capacitance is increased. It takes more electrons to charge both the body and the lamp, and the circuit detects that difference. It is even possible to purchase plug-in boxes that work on the same principle and can turn any lamp into a touch-sensitive lamp.
Many touch-sensitive lamps have three brightness settings even though they do not use three-way bulbs. The circuit changes the brightness of the lamp by changing the “duty cycle” of the power reaching the bulb. A bulb with a normal light switch gets “full power”. Rapidly switching the bulb on and off is the basic idea used to change the brightness of the lamp—the circuit uses zero percent (off), 33 percent, 66 percent and 100 percent duty cycles to control the lamp's brightness.
It is also known to incorporate interactive devices such as touch screens with display devices rather than area illuminators to provide pointing information as with a keyboard or mouse. Displays such as LCDs can incorporate an electroluminescent backlight that is not electronically connected to the touch screen directly and are not used for “general lighting” purposes but to illuminate the LCD display.
Touch screen monitors have become more and more commonplace, as their price has steadily dropped over the past decade. There are three basic systems that are used to recognize a person's touch: resistive, capacitive, and surface acoustic wave (SAW). Infrared and inductive systems, though less popular, are also known.
The resistive system consists of a normal glass panel that is covered with a uniformly conductive and a deformable top sheet with a similarly conductive layer. These two layers are held apart by spacers, and a scratch-resistant layer is placed on top of the apparatus. An electrical potential is placed across the two layers while the monitor is operational. When a user touches the deformable top sheet, the two conductive layers make contact in that exact spot. The change in the electrical field is noted and the coordinates of the point of contact are calculated by the computer. Once the coordinates are known, a special driver translates the touch into location information, much as a computer mouse driver translates a mouse's movements into a click or a drag.
In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch screen driver software. One advantage that the capacitive system has over the resistive system is that it transmits almost 90 percent of the light from the monitor, whereas the resistive system only transmits about 75 percent. This gives the capacitive system a much clearer picture than the resistive system.
On the monitor of a surface acoustic wave system, two transducers (one receiving and one sending) are placed along the x and y axes of the monitor's glass plate.
Also placed on the glass are reflectors that reflect an electrical signal sent from one transducer to the other. The receiving transducer measures any disturbance by a touch event at any instant, and can locate it accordingly. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics (other systems have significant degradation in clarity).
These interactive systems also differ in which stimuli will register as a touch event. A resistive system registers a touch as long as the two layers make contact, which means that it responds to any deforming object, whether a stylus or a finger. A capacitive system, on the other hand, must have a conductive input, usually a finger, in order to register a touch. The surface acoustic wave system works much like the resistive system, allowing a touch with almost any object—except hard and small objects such as pen tips. Typically, resistive systems are the least expensive, have the lowest clarity, and are most easily damaged by sharp objects. The surface acoustic wave system is usually the most expensive. However, such devices are not adapted to area illumination and are, moreover expensive, complex, and are not readily adapted to the environment and user interface.
A wide variety of these systems are known in the art and are described, for example, in “Being Seen Technologies Inc.” at http://www.beingseen.com/index.html, “Novatech electro-luminescent” at http://www.novael.com/index.html, “MetroMark” at http://www.metromark.com, and “Luminousfilm” at http://www.luminousfilm.com.
However, none of these designs provide a convenient local control for a flat-panel area illuminator that does not require additional mounting equipment and is not location specific.